You may not want to hear this, but I have suffered from Burning Mouth Syndrome (BMS) for about 10 years. It usually affects women over 50, there appears to be no known cause, and there is no cure as such. You may have already seen this but it gives a good description of BMS.
My problems started when I thought I had a throat infection, and my GP tried me on several different ABs. After the third lot of ABs, I started to get terrible burning in my mouth, and was convinced I had oral cancer. Was referred for tests at hospital, and ENT consultant mentioned BMS, the first I'd heard of it.
It is sometimes related to dental work, and I had had a tooth extracted a month before the throat problem arose (which turned out eventually to be thyroid nodules), and is also associated with excessive doses of ABs, so I ticked both of those boxes. Apparently, it can disappear as suddenly as it started, but I still suffer after 10 years, and have just learned to live with it.
I found that coffee, alcohol and cigarettes aggravate it (and am guilty of all three!) and that although it isn't all that bad first thing in the morning, it gets progressively worse through the day - all typical of BMS. Spicy food with chilli in it will also make it worse, I also get a metallic taste too.
I do hope that you have something entirely different, CasaBevron, as it's a wretched condition, but more common than you would think.